tests/test-gendoc-da.t

pathutil: use `finddirs_rev_noroot` instead of `parts`

The benefit this brings is very tiny, if it's even there,
since we still didn't get rid of the [parts] computation.

It probably won't be worth it without the subsequent patch
that adds one more use of [finddirs_rev_noroot]

#require docutils gettext

  $ $TESTDIR/check-gendoc da
  checking for parse errors